I. Field of the Invention
The disposal of solid waste material, particularly hazardous waste material, is a continuing problem. Hazardous waste materials must be properly handled to avoid damage to humans and the environment.
This invention relates to a method and apparatus for the reduction of solid waste material using coherent radiation. More particularly, this invention relates to a method and apparatus for reducing solid waste material to a slag-like composition using a plasma energized by coherent radiation.
The solid waste material may be combustible excitation material or, the solid waste may itself be the product of prior combustion such as incinerator ash. The ash or like material is processed with combustible excitation material which itself may be a waste material.
The combination of combustible excitation material and the products of prior combustion are heated in a plasma of sufficient volume and temperature to reduce the waste to a relatively harmless disposable slag-like material and an effluvia of gas and particulates. The effluvia is cleansed of harmful materials, such as products of incomplete combustion (PICs) and heavy metals, and otherwise processed for ready disposition. The slag-like product of the present invention is pebble-like hard material which is environmentally safe.
Incineration of waste material is a principal method of waste disposal. However, the ash by-product of incineration (commonly called fly ash or bottom ash) is itself considered to be hazardous waste since it contains heavy metals and other hazardous substances such as arsenic and dioxins. Such substances are dangerous to humans and will contaminate the environment unless the ash is disposed of in a safe manner. Safe disposal is costly and itself represents an ever present risk to the environment. It is therefore desirable to provide a method and apparatus for further reducing fly ash and similar incinerated waste to materials which are relatively more suitable for environmentally safe disposal or even as useful products. It is also desirable to provide a method and apparatus for the reduction of solid waste materials which are considered to be extremely hazardous such as solid medical wastes. The present invention is directed to a method and apparatus for the reduction of such solid waste materials using coherent radiation.
II. Description of the Prior Art
Methods and apparatus for reducing to separable constituents, including waste materials, using coherent radiation have been proposed in the past but none is known to be practicable. The reduction of solid materials in a plasma is also known although such plasmas are not necessarily initiated and sustained by directing coherent radiation at the material to be reduced to separable constituents.
Other deficiencies in high temperature waste reduction processes have limited their utility. These involve difficulties in processing the effluvia of the combustion process which are themselves hazardous and therefore require costly special treatment.
III. Summary of the Invention
In accordance with the present invention, coherent radiation is used to provide the energy to excite and sustain a plasma in which solid waste is reduced to a slag-like material from which has been removed the more harmful constituents. The solid waste material may be conventional solid wastes but the present invention is principally intended for the reduction of the ash by-product of prior incineration, known as fly ash or bottom ash. The effluvia of the plasma reduction process take the form of particulates and gaseous by-products of the reduction process. In accordance with the present invention, the particulates are scrubbed and filtered from the effluvia. The gas is processed to destroy or chemically convert harmful constituents. The remaining gas is then safely exhausted into the atmosphere.
Thus the present invention is directed to a method and apparatus for the reduction of solid waste material in a plasma, especially incinerator ash, using coherent radiation as the source of energy for the plasma. The plasma is sustained at an useful volume by adding to the solid waste, as necessary, an aggregate of more readily combustible excitation materials. Preferably these combustible excitation waste materials are waste materials (herein excitation waste) which have not yet been burned. Examples of excitation waste are metal and wood chips resulting from manufacturing processes.
The present invention has particular utility in that it uses coherent radiation produced by a laser at relatively low power levels. Excitation of the plasma is obtained and sustained, and the acceptability of the atmospherically exhausted gases is determined as part of the process. The coherent radiation is provided by a relatively low power CO.sub.2 laser.
In accordance with the present invention solid waste material, especially a product of prior incineration, is heated in a plasma of proper size causing the material to disassociate and reassociate into a slag-like material and an effluvia of gas and particulates. The plasma is excited by coherent radiation, and where the waste material is fly ash or the like, combustible wastes are included to help excite the plasma. The present invention is particularly directed to the reduction of solid waste material. The excitation wastes are in part excited and reduced in a secondary reaction chamber which serves to heat the effluvia to destroy products of incomplete combustion (PICs) by chemical reaction or disassociation and reassociation into less harmful materials which can be processed or otherwise converted to carbon dioxide (CO.sub.2), water and salts. The molten product of the secondary reaction chamber flows into the primary chamber where the fly ash is excited by coherent radiation and converted into slag an the effluvia.
The apparatus for accomplishing the process includes a primary reaction chamber within which the solid waste material is heated in a plasma excited by a laser; a secondary reaction chamber wherein the excitation waste is heated and wherein further reduction of the effluvia takes place electrostatic scrubbers for removing particulates and certain metals from the effluvia; and a gas treatment process.
The slag-like product of the present invention is produced in small pebbles which are relatively free of contaminants and therefore can be safely disposed of.